The correct answer is at least four, located in Arizona, California and Virginia, according to his staff. Newsweek estimated this summer that the couple owns at least seven properties.

And a Politico analysis later in the day found McCain's family owns at least eight properties, according to property and tax records, as well as interviews.

In recent weeks, Democrats have stepped up their effort to caricature McCain as living an outlandishly rich lifestyle — a bit of payback to the GOP for portraying Sen. Barack Obama (D-Ill.) as an elitist, and for turning the spotlight in 2004 on the five homes owned by Sen. John F. Kerry (D-Mass.) and his wife, Teresa Heinz Kerry.

Pro-Obama labor groups have sent out mailers highlighting McCain’s wealth, and prominent Democrats have included references to it in comments to reporters.

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Twice in the past two weeks, those Democrats have focused on McCain’s houses.

Sen. Charles Schumer (D-N.Y.) told Politico’s Ben Smith that it was McCain “who wears $500 shoes, has six houses and comes from one of the richest families in his state."

And David Axelrod, Obama’s chief strategist, referred in an interview with Adam Nagourney of The New York Times to an imagined meeting of McCain strategists “on the portico of the McCain estate in Sedona — or maybe in one of his six other houses.”

The Obama campaign seized on the house issue Thursday with an ad called "Seven," claiming that's the number of houses McCain has. The ad closes with a shot of the White House and the narration: "Here's ONE house American can't afford to let John McCain move into."

McCain spokesman Brian Rogers said in response: "Does a guy who made more than $4 million last year, just got back from vacation on a private beach in Hawaii and bought his own million-dollar mansion with the help of a convicted felon really want to get into a debate about houses? Does a guy who worries about the price of arugula and thinks regular people 'cling' to guns and religion in the face of economic hardship really want to have a debate about who’s in touch with regular Americans?

“The reality is that Barack Obama’s plans to raise taxes and opposition to producing more energy here at home as gas prices skyrocket show he’s completely out of touch with the concerns of average Americans.”

At a campaign appearance in Chester, Va., on Thursday morning, Obama said: "Somebody asked John McCain, 'How many houses do you have?’ And he said, I’m not sure. I’ll have to check with my staff. True quote: I’m not sure, I’ll have to check with my staff. So they asked his staff and he said, at least four. At least four! ...

"If you’re like me and you’ve got one house – or you were like the millions of people who are struggling right now to keep up with their mortgage so that they don’t lose their home — you might have a different perspective. By the way, the answer is: John McCain has seven homes. So there’s just a fundamental gap of understanding between John McCain's world and what people are going through every single day here in America."

McCain’s comments came four days after he initially told Pastor Rick Warren during a faith forum on Sunday his threshold for considering someone rich is $5 million — a careless comment he quickly corrected.

In the interview, McCain did not offer an alternate number, but had a new answer ready. “I define rich in other ways besides income,” he said. “Some people are wealthy and rich in their lives and their children and their ability to educate them. Others are poor if they’re billionaires.”

McCain, by anyone's measure, is well-off, if you account for his wife's fortune. Cindy McCain inherited control of her father’s beer distributorship, the largest in Arizona, and has an estimated worth of more than $100 million.